NIDA has identified principles of effective treatment for substance abusers and the "Andrews Group" has identified principles of effective rehabilitative correctional treatment. Although there are individual studies to support the principles identified by NIDA for substance abusers and there are meta-analytic studies by the Andrews group on corrections-based treatment, no systematic review or meta-analysis of the full research literature has been conducted to verify principles of effective treatment for substance abusers. In previous studies, the research teams from NDRI and ISAP developed two meta-analytic databases containing hundreds of primary research studies of treatment for substance abusers, and these databases contain variables that can be used to test nine of the principles of treatment: six of the thirteen NIDA principles and all three of the Andrews group's principles. The primary aim of this study is to conduct a methodologically strong test of these nine principles. The method employed is systematic reviews and meta-analyses of the existing NDRI and ISAP meta-analytic databases, expanded to include recent studies to be collected for this project. An estimated total of 700 studies of treatment effectiveness will be available for meta-analyses. A secondary aim is to strengthen meta-analytic techniques and improve the methodological quality by (a) identifying sources of inconsistencies in meta-analyses conducted on the same topic and recommending improved protocols, (b) adapting and validating improved measures of the methodological quality of primary research studies, and (c) evaluating the use of different methods for dealing with missing data. The project has implications for practice as it will provide researchers and practitioners substantially more knowledge of (1) which principles of treatment are indeed effective in improving client outcomes, possibly under specific moderating factors (e.g., with specific types of clients), and (2) the scientific strength and limitations of meta-analysis using current protocols and how this essential method can be improved.